Effects of Zr ion implantation on crystal structure and nanoindentation behavior of TC18 titanium alloy

In this study, TC18 titanium alloy was ion implanted with Zr ions to a fluence of 3.56 x 10(16), 5.53 x 10(16) and 7.12 x 10(16) ions cm(-2). The surface morphologies were characterized by the scanning electron microscopy (SEM) and atomic force microscope (AFM). The crystal structure of the Zr implanted TC18 titanium alloy was evaluated by the x-ray diffraction (XRD) and the corresponding calculations were used to analysis the nanoindentation behavior. Nanoindentation tests with different loads (5 mN, 10 mN and 15 mN) were used to investigate the nanoindentation behavior of samples. Zr ion implantation not only affected the surface microstructures of substrate, but also affected the crystal structure. When the implantation fluence was 3.56 x 10(16) ions cm(-2), the surface roughness of sample was reduced, while the residual compressive stress caused the XRD peak shift to higher angle compared with the baseline of substrate. The irradiation effect increases with increasing implantation fluence which led to generation of etch pits and cracks, and therefore increased surface roughness of TC18 titanium alloy. At the same time, the increase of lattice parameters shifted the XRD peak to low angle. The result of nanoindentation test showed that Zr solid solution strengthening improved the hardness of substrate. However, the dislocation density gradually decreased with the increasing of implantation fluence, which therefore reduced the nanohardness of samples. The highest hardness values of TC18 titanium alloy under different indentation loads were all found in samples treated with the ion fluence of 3.56 x 10(16) ions cm(-2), as a result of Zr solid solution strengthening and high dislocation density.